Antipsychotic drugs have been used not only in the treatment of schizophrenia but also in the treatment of troublesome behaviors (for example, aggressive actions, mental excitation, dromomania, delirium) caused by cerebrovascular disorders or senile dementia. However, conventional antipsychotic drugs are accompanied by severe extrapyramidal disorders as side effects, which results in a serious problem.
In recent years, there have been made approaches for developing antipsychotic drugs from a viewpoint completely differing from the functional mechanism of the conventional drugs to thereby solve the above-mentioned problem. One of these approaches includes the use of a sigma receptor antagonist. A compound having a specific affinity for a sigma receptor, which is considered as an receptor participating in mental symptoms such as hallucinosis, exhibits an antipsychotic action without causing any extrapyramidal disorders.
There has been known talipexole (a compound described in JP-B-52-46236) as an antipsychotic drug having a thiazole skeleton. It is reported that this compound is a selective dopamine autoreceptor agonist and suppresses nerve ignition and biosynthesis and liberation of dopamine by stimulating the presynaptic autoreceptor, thus depressing the function of the dopamine nerve system, which closely relates to the outbreak of schizophrenia European Journal of Pharmacology, 166, 303-305 (1989); Acta Pharmaceut. Suec. Suppl., 1, 154-164 (1983)!.
However, it cannot be expected too much of talipexole of being highly effective on positive symptoms of schizophrenia, similar to other conventionally known selective dopamine autoreceptor agonists. In addition, the effect of talipexole on negative symptoms of this disease had not been definitely confirmed Toshiya Inada et al., Shinkei Seishin Yakuri, 13, 75-77 (1990)!.
In contrast thereto, the compound of the present invention has an affinity for a sigma receptor. Thus it is considered as being different from the dopamine autoreceptor agonists in functional mechanism.
An object of the present invention is to provide an antipsychotic drug which is different from dopamine autoreceptor agonists in functional mechanism, namely, an antipsychotic drug having a specific affinity for a sigma receptor and causing no extrapyramidal disorder.